1. Field of the Invention
The present invention relates to a microstrip reflective array antenna and, more particularly, to a microstrip reflective array antenna adopting a plurality of U-slot patches.
2. Description of Related Art
The reflective array antenna has the advantages of being both easy to manufacture and having centralization of reflected microwave signals, thus it is popularly used to receive and transmit microwave signals. As shown in FIG. 1, the U.S. Pat. No. 6,195,047/B1, entitled “Integrated microelectromechanical phase shifting reflective array antenna”, discloses a traditional reflective array antenna 10, comprising a traditional circular disk 12 and a horn antenna 16. A plurality of array units 14 of the traditional circular disk 12 reflect microwave signals transmitted from far away, then centralize and reflect the microwave signals to the horn antenna 16, and finally the horn antenna 16 receives the microwave signals. As a result, better signal gain and wider communication band are achieved. As shown in FIG. 2, the plurality of array units 14 can be disposed on the upper surface of the substrate 18 via printed circuit technology. The lower surface of the substrate 18 comprises a grounding layer 19, preferably a metal layer. Due to the necessary gap between the traditional circular disk 12 and the horn antenna, a support extends therebetween, thus retaining and stabilizing the horn antenna 16 on top of the traditional circular disk 12. To attain the purpose of centralizing and reflecting microwave signals, the plurality of array units 14 requires a unique design to reflect the microwave signals to the position of the horn antenna 16. Therefore, the relative positions of the horn antenna 16 and the traditional circular disk 12 must be fixed. As known, when the traditional reflect array antenna 10 transmits microwave signals, they are transmitted by the horn antenna 16 and reflected to the far end by the traditional circular disk 12.
To attain the purpose of centralizing and reflecting of microwave signals, the patterns of the plurality of array units 14 are not identical. As shown in FIG. 3, each of array units 141, 142, and 144 comprises a delay line of different length whereas array unit 143 comprises no delay line. The function of the delay line is to adjust the phase of microwave signals to determine the main beam direction in which the array unit 14 reflects, making the microwave signals reflected by the array unit 14 centralize to the horn arena 16.
However, the traditional reflect array antenna 10 has disadvantages such as limited signal gain and narrow communication bandwidth.